Grade For A Mark

Write the body of grade_for(mark: int) -> str so it returns A for 90 or more, B for 80 up to 89, C for 70 up to 79, D for 60 up to 69 and F for anything lower, with one if / elif / else chain. Do NOT write a main block or any top-level test code; the tests construct the calls. Input: one line, an integer mark, which the tests read and pass to your function before printing the letter it returns.